Typical engines, such as internal combustion engines, include at least one piston that reciprocates within a cylinder of the engine. The piston includes a head portion, a skirt, and at least one side panel. The head portion usually includes at least one piston ring groove for receiving a piston ring therein.
The piston is generally sized to be just smaller in overall diameter than the diameter of the cylinder in which the piston reciprocates. This allows the piston to move within the cylinder while minimizing the noise in the engine. When too much space exists between the piston and cylinder, a disruptive noise, commonly known as piston slap, can occur as the piston moves within the cylinder. It is desirable to reduce the amount of piston slap that occurs within the engine.
When the piston moves within the cylinder, some of the piston surfaces can rub against the inner surface of the cylinder, especially when the tolerances between the size of the piston and the diameter of the cylinder are very close. Many engines are cast from an aluminum alloy, which provides a lightweight but strong engine housing. When the piston is cast from the same material as the engine housing (and thus, the same material as the cylinder), scuffing can occur between the surfaces of the piston and the cylinder, thereby decreasing the life of the piston, increasing the piston slap, and also increasing emissions. It is therefore desirable to provide a bearing surface on either the cylinder or the piston that will reduce the wear on the piston.